The disproportionation of aromatic hydrocarbons in the presence of zeolite catalyst was reported by Grandio et al in the OIL AND GAS JOURNAL, Vol. 69, No. 48 (1971). Specific catalytic processes for disproportionation of toluene have been described in, for example, U.S. Pat. Nos. 4,160,788; 4,182,923 and 4,456,780.
Toluene disproportionation involves the conversion of toluene to benzene and xylene isomers, including ortho-, meta-and para-xylene. Meta-xylene is the least desired product, whereas, ortho- and para-xylene are the most desired isomers. Para-xylene, in substantial yield, is of particular value in the manufacture of terephthalic acid which is an intermediate in the manufacture of synthetic fibers such as "DACRON".